Electroacoustic transduction film and manufacturing method thereof, electroacoustic transducer, flexible display, vocal cord microphone, sensor for musical instrument

ABSTRACT

Provided are an electroacoustic transduction film capable of reproducing a sound with a sufficient sound volume at a high conversion efficiency, a manufacturing method thereof, an electroacoustic transducer, a flexible display, a vocal cord microphone, and a sensor for a musical instrument. The electroacoustic transduction film includes: a polymer composite piezoelectric body in which piezoelectric body particles are dispersed in a viscoelastic matrix formed of a polymer material having viscoelasticity at a normal temperature; two thin film electrodes laminated on both surfaces of the polymer composite piezoelectric body; and two protective layers respectively laminated on the two thin film electrodes, in which an intensity ratio α1=(002) plane peak intensity/((002) plane peak intensity+(200) plane peak intensity) between a (002) plane peak intensity and a (200) plane peak intensity derived from the piezoelectric body particles in a case where the polymer composite piezoelectric body is evaluated by an X-ray diffraction method is more than or equal to 0.6 and less than 1.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of copending application Ser. No.15/868,146, filed on Jan. 11, 2018, which is the Continuation of PCTInternational Application No. PCT/JP2016/071392 filed on Jul. 21, 2016,which claims the benefit under 35 U.S.C. § 119(a) to Patent ApplicationNo. 2015-147608, filed in Japan on Jul. 27, 2015, and to PatentApplication No. 2016-001221, filed in Japan on Jan. 6, 2016 all of whichare hereby expressly incorporated by reference into the presentapplication.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an electroacoustic transduction filmused for an acoustic device such as a speaker, a manufacturing method ofthe electroacoustic transduction film, an electroacoustic transducerwhich uses the electroacoustic transduction film, a flexible display, avocal cord microphone, and a sensor for a musical instrument.

2. Description of the Related Art

In response to thinning and a reduction in weight of displays such asliquid crystal displays and organic electroluminescence (EL) displays,speakers used in such thin displays are also required to be lighter andthinner. In addition, in response to the development of flexibledisplays using a flexible substrate made of plastic or the like,speakers used therein are also required to be flexible.

Here, as the shape of a speaker of the related art, a so-called coneshape such as a funnel-like shape, a spherical dome-like shape, and thelike are generally used. However, in a case where such a speaker isembedded in the thin display described above, there is concern thatthinning may not be sufficiently achieved and lightweight properties andflexibility may be impaired. In addition, in a case where the speaker isattached to the outside of the thin display, it is difficult to carrythe thin display.

Here, as a speaker which is thin and is able to be integrated with athin display or a flexible display without impairing the lightweightproperties or flexibility, it has been proposed to use a piezoelectricfilm which has flexibility in the form of a sheet and has a propertythat stretches and contracts in response to an applied voltage.

Here, the present applicants suggested, as a piezoelectric film whichhas flexibility in the form of a sheet and is able to stably reproduce asound with high acoustic quality, an electroacoustic transduction filmdisclosed in JP2014-14063A. The electroacoustic transduction filmdisclosed in JP2014-14063A includes a polymer composite piezoelectricbody (piezoelectric layer) in which piezoelectric body particles aredispersed in a viscoelastic matrix formed of a polymer material havingviscoelasticity at a normal temperature, thin film electrodes formed onboth surfaces of the polymer composite piezoelectric body, andprotective layers formed on the surfaces of the thin film electrodes.

In such an electroacoustic transduction film, a ferroelectric materialsuch as PZT (lead zirconate titanate) is used as piezoelectric bodyparticles. The crystal structure of the ferroelectric material isdivided into many domains (domains) with different spontaneouspolarization directions. In this state, the spontaneous polarization ineach domain and the correspondingly generated piezoelectric effectcancel each other, so that no piezoelectric properties are seen as awhole.

The spontaneous polarization directions of the domains are aligned(oriented) by performing electric polarization processing such as coronapoling and externally applying an electric field with a certain value ormore. The piezoelectric body particles subjected to the electricpolarization processing exhibit the piezoelectric effect in response tothe externally applied electric field.

In the electroacoustic transduction film, since the piezoelectric layercontains the piezoelectric body particles having such piezoelectricproperties, the transduction film itself stretches and contracts in thesurface direction thereof in response to an applied voltage and vibratesin a direction perpendicular to the surface, thereby performing aconversion between a vibration (sound) and an electrical signal.

SUMMARY OF THE INVENTION

In order to further improve a sound pressure (conversion efficiency) insuch an electroacoustic transduction film, the present inventorsconsidered a further increase in the orientation of each domain in thepiezoelectric body particles through polarization processing for afurther increase in piezoelectric properties.

In general, an X-ray diffraction method (XRD) is used as a method foranalyzing a crystal structure, and the arrangement of atoms in crystalsis examined by XRD.

Here, as an index of the orientation, the intensity ratio: (002) planepeak intensity/((002) plane peak intensity+(200) plane peak intensity)between a (002) plane peak intensity and a (200) plane peak intensityderived from the piezoelectric body particles in a case where thepolymer composite piezoelectric body is evaluated by the X-raydiffraction method was used, and a further improvement in the soundpressure of the electroacoustic transduction film was examined bycontrolling the intensity ratio.

Here, in Ferroelectrics Volume 62, Issue 1, 167, (1985), it is describedthat the ratio between a (002) plane peak intensity and a (200) planepeak intensity is controlled by increasing a poling electric fieldduring electric polarization processing. However, there is a limit tothe control to increase the poling electric field during electricpolarization processing, and the intensity ratio: (002) plane peakintensity/((002) plane peak intensity+(200) plane peak intensity) issaturated at around 0.55, and a higher intensity ratio cannot beobtained. Therefore, a higher conversion efficiency could not beobtained, and a higher sound pressure could not be obtained.

An object of the present invention is to solve such a problem of therelated art, and is to provide an electroacoustic transduction filmcapable of reproducing a sound with a sufficient sound volume at a highconversion efficiency, a manufacturing method thereof, anelectroacoustic transducer, a flexible display, a vocal cord microphone,and a sensor for a musical instrument.

The present inventors have intensively studied to attain the object, andfound that by providing a polymer composite piezoelectric body in whichpiezoelectric body particles are dispersed in a viscoelastic matrixformed of a polymer material having viscoelasticity at a normaltemperature, two thin film electrodes laminated on both surfaces of thepolymer composite piezoelectric body, and two protective layersrespectively laminated on the two thin film electrodes, and by causingan intensity ratio α₁=(002) plane peak intensity/((002) plane peakintensity+(200) plane peak intensity) between a (002) plane peakintensity and a (200) plane peak intensity derived from thepiezoelectric body particles in a case where the polymer compositepiezoelectric body is evaluated by an X-ray diffraction method to bemore than or equal to 0.6 and less than 1, the problem can be solved,thereby completing the present invention.

That is, the present invention provides an electroacoustic transductionfilm having the following configuration, a manufacturing method thereof,an electroacoustic transducer using the electroacoustic transductionfilm, a flexible display, a vocal cord microphone, and a sensor for amusical instrument.

(1) An electroacoustic transduction film comprising: a polymer compositepiezoelectric body in which piezoelectric body particles are dispersedin a viscoelastic matrix formed of a polymer material havingviscoelasticity at a normal temperature; two thin film electrodeslaminated on both surfaces of the polymer composite piezoelectric body;and two protective layers respectively laminated on the two thin filmelectrodes, in which an intensity ratio α₁=(002) plane peakintensity/((002) plane peak intensity+(200) plane peak intensity)between a (002) plane peak intensity and a (200) plane peak intensityderived from the piezoelectric body particles in a case where thepolymer composite piezoelectric body is evaluated by an X-raydiffraction method is more than or equal to 0.6 and less than 1.

(2) The electroacoustic transduction film according to (1), in which theintensity ratio α₁ is more than or equal to 0.67 and less than or equalto 0.75.

(3) The electroacoustic transduction film according to (1) or (2), inwhich the polymer material has a cyanoethyl group.

(4) The electroacoustic transduction film according to any one of (1) to(3), in which the polymer material is cyanoethylated polyvinyl alcohol.

(5) A manufacturing method of an electroacoustic transduction filmincluding a polymer composite piezoelectric body in which piezoelectricbody particles are dispersed in a viscoelastic matrix formed of apolymer material having viscoelasticity at a normal temperature, twothin film electrodes laminated on both surfaces of the polymer compositepiezoelectric body, and two protective layers respectively laminated onthe two thin film electrodes, the method comprising: a preparation stepof preparing electrode laminated bodies in each of which one of the thinfilm electrodes and one of the protective layers are laminated; a firstlamination step of producing a first laminated body by laminating one ofthe electrode laminated bodies and the polymer composite piezoelectricbody; an electric polarization processing step of performing electricpolarization processing on the polymer composite piezoelectric body ofthe first laminated body; a second lamination step of producing a secondlaminated body by laminating the other electrode laminated body on thesurface of the polymer composite piezoelectric body on which noelectrode laminated body is laminated; and a mechanical polarizationprocessing step of performing mechanical polarization processing on thesecond laminated body.

(6) The manufacturing method of an electroacoustic transduction filmaccording to (5), in which, in the mechanical polarization processingstep, the mechanical polarization processing is performed by applying ashear stress to the second laminated body using a roller.

(7) The manufacturing method of an electroacoustic transduction filmaccording to (6), in which, in the mechanical polarization processingstep, the shear stress applied of the second laminated body is 0.3 MPato 0.5 MPa.

(8) The manufacturing method of an electroacoustic transduction filmaccording to any one of (5) to (7), in which, in the electricpolarization processing step, the electric polarization processing isperformed by corona poling processing.

(9) An electroacoustic transducer comprising: the electroacoustictransduction film according to any one of (1) to (4).

(10) A flexible display comprising: the electroacoustic transductionfilm according to any one of (1) to (4) attached to a surface of theflexible display having flexibility, the surface being opposite to animage display surface.

(11) A vocal cord microphone comprising: the electroacoustictransduction film according to any one of (1) to (4) used as a sensor.

(12) A sensor for a musical instrument comprising: the electroacoustictransduction film according to any one of (1) to (4) used as a sensor.

According to the present invention, it is possible to provide thecapable of reproducing a sound with a sufficient sound volume at a highconversion efficiency, the manufacturing method thereof, theelectroacoustic transducer, the flexible display, the vocal cordmicrophone, and the sensor for a musical instrument.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically illustrating an example of anelectroacoustic transduction film of the present invention.

FIG. 2A is a conceptual view illustrating an example of a manufacturingmethod of the electroacoustic transduction film.

FIG. 2B is a conceptual view illustrating the example of themanufacturing method of the electroacoustic transduction film.

FIG. 2C is a conceptual view illustrating the example of themanufacturing method of the electroacoustic transduction film.

FIG. 2D is a conceptual view illustrating the example of themanufacturing method of the electroacoustic transduction film.

FIG. 2E is a conceptual view illustrating the example of themanufacturing method of the electroacoustic transduction film.

FIG. 3 is a conceptual view illustrating an example of a mechanicalpolarization processing step.

FIG. 4A is a sectional view schematically illustrating an example of anelectroacoustic transducer of the present invention.

FIG. 4B is a sectional view taken along line B-B in FIG. 4A.

FIG. 5 is a sectional view conceptually illustrating another example ofthe electroacoustic transducer of the present invention.

FIG. 6A is a sectional view illustrating another example of theelectroacoustic transducer of the present invention.

FIG. 6B is a sectional view illustrating another example of theelectroacoustic transducer of the present invention.

FIG. 6C is a sectional view illustrating another example of theelectroacoustic transducer of the present invention.

FIG. 6D is a sectional view illustrating another example of theelectroacoustic transducer of the present invention.

FIG. 7A is a view conceptually illustrating an example of a flexibledisplay of the present invention, and illustrates an organic EL display.

FIG. 7B is a view conceptually illustrating an example of the flexibledisplay of the present invention, and illustrates an electronic paper.

FIG. 7C is a view conceptually illustrating an example of the flexibledisplay of the present invention, and illustrates a liquid crystaldisplay.

FIG. 8 is a view conceptually illustrating a configuration of a generalvocal cord microphone.

FIG. 9 is a conceptual view illustrating a method of measuring a soundpressure sensitivity in examples.

FIG. 10 is a graph showing XRD patterns in examples and comparativeexamples.

FIG. 11A is a graph showing the relationship between an intensity ratioα₁ and a sound pressure sensitivity.

FIG. 11B is a graph showing the relationship between an intensity ratioα₁ and a sound pressure sensitivity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an electroacoustic transduction film, a manufacturingmethod thereof, an electroacoustic transducer, a flexible display, avocal cord microphone, and a sensor for a musical instrument of thepresent invention will be described in detail based on the preferredembodiments shown in the accompanying drawings.

Descriptions of the constituent elements described below may be madebased on representative embodiments of the present invention, but thepresent invention is not limited to the embodiments.

In this specification, a numerical range expressed by using “to” means arange including numerical values described before and after “to” as alower limit and an upper limit.

As will be described later, the electroacoustic transduction film of thepresent invention is used as a vibration plate of the electroacoustictransducer.

In the electroacoustic transducer, in a case where the electroacoustictransduction film is stretched in an in-plane direction due to theapplication of a voltage to the electroacoustic transduction film, theelectroacoustic transduction film moves upward (in the radial directionof sound) in order to absorb the stretching. Conversely, in a case wherethe electroacoustic transduction film is contracted in the in-planedirection due to the application of a voltage to the electroacoustictransduction film, the electroacoustic transduction film moves downward(toward a case) in order to absorb the contraction. The electroacoustictransducer performs a conversion between a vibration (sound) and anelectrical signal by the vibrations caused by repetition of stretchingand contraction of the electroacoustic transduction film, and is used toreproduce a sound from a vibration in response to an electrical signalby inputting the electrical signal to the electroacoustic transductionfilm, convert a vibration of the electroacoustic transduction film fromthe received sound waves into an electrical signal, or impart tactilityor transport an object from vibrations.

Specifically, various acoustic devices including a speaker such as afull-range speaker, a tweeter, a squawker, and a woofer, a speaker for aheadphone, a noise canceller, a microphone, a pickup used in musicalinstruments including a guitar, and the like can be cited. In addition,the electroacoustic transduction film of the present invention is anon-magnetic body, and thus is able to be suitably used as a noisecanceller for MRI among other noise cancellers.

Furthermore, the electroacoustic transducer of the present invention isthin, lightweight, and bendable, and thus is suitably used in wearableproducts such as hats, mufflers and clothes, thin displays such astelevisions and digital signages, ceilings of buildings and automobiles,curtains, umbrellas, wallpapers, windows, beds, and the like.

FIG. 1 is a sectional view schematically illustrating an example of theelectroacoustic transduction film of the present invention.

As illustrated in FIG. 1, an electroacoustic transduction film(hereinafter, also referred to as “transduction film”) 10 of the presentinvention has a piezoelectric layer 12 which is a sheet-like materialhaving piezoelectric properties, a lower thin film electrode 14laminated on one surface of the piezoelectric layer 12, a lowerprotective layer 18 laminated on the lower thin film electrode 14, anupper thin film electrode 16 laminated on the other surface of thepiezoelectric layer 12, and an upper protective layer 20 laminated onthe upper thin film electrode 16.

Here, in the transduction film 10 of the present invention, in a casewhere the piezoelectric layer 12 formed of the polymer compositepiezoelectric body is evaluated by an X-ray diffraction method, theintensity ratio α₁=(002) plane peak intensity/((002) plane peakintensity+(200) plane peak intensity) between a (002) plane peakintensity and a (200) plane peak intensity derived from thepiezoelectric body particles is more than or equal to 0.6 and less than1.

These points will be described in detail later.

In the transduction film 10, the piezoelectric layer 12 which is apolymer composite piezoelectric body, as conceptually illustrated inFIG. 1, is a polymer composite piezoelectric body in which piezoelectricbody particles 26 are uniformly dispersed in a viscoelastic matrix 24formed of a polymer material having viscoelasticity at a normaltemperature. Furthermore, herein, the “normal temperature” indicates atemperature range of approximately 0° C. to 50° C.

Although described later, the piezoelectric layer 12 is subjected topolarization processing.

Here, it is preferable that the polymer composite piezoelectric body(the piezoelectric layer) 12 has the following requisites.

(i) Flexibility

For example, in a case of being gripped in a state of being loosely bentlike a newspaper or a magazine as a portable device, the polymercomposite piezoelectric body is continuously subjected to large bendingdeformation from the outside at a comparatively slow vibration of lessthan or equal to a few Hz. At this time, in a case where the polymercomposite piezoelectric body is hard, large bending stress is generatedto that extent, and a crack is generated at the interface between thepolymer matrix and the piezoelectric body particles, possibly leading tobreakage. Accordingly, the polymer composite piezoelectric body isrequired to have suitable flexibility. In addition, in a case wherestrain energy is diffused into the outside as heat, the stress is ableto be relieved. Accordingly, the loss tangent of the polymer compositepiezoelectric body is required to be suitably large.

(ii) Acoustic Quality

In the speaker, the piezoelectric body particles vibrate at a frequencyof an audio band of 20 Hz to 20 kHz, and the entire vibration plate (thepolymer composite piezoelectric body) integrally vibrates due to thevibration energy such that a sound is reproduced. Accordingly, in orderto increase the transmission efficiency of the vibration energy, thepolymer composite piezoelectric body is required to have suitablehardness. In addition, in a case where the frequency properties of thespeaker become smooth, the changed amount of the acoustic quality at thetime of when the lowest resonance frequency f₀ changes according to achange in the curvature also decreases. Accordingly, the loss tangent ofthe polymer composite piezoelectric body is required to be suitablylarge.

As described above, the polymer composite piezoelectric body is requiredto be rigid with respect to a vibration of 20 Hz to 20 kHz, and beflexible with respect to a vibration of less than or equal to a few Hz.In addition, the loss tangent of the polymer composite piezoelectricbody is required to be suitably large with respect to the vibration ofall frequencies of less than or equal to 20 kHz.

In general, a polymer solid has a viscoelasticity relieving mechanism,and a molecular movement having a large scale is observed as a decrease(relief) in a storage elastic modulus (Young's modulus) or the localmaximum (absorption) in a loss elastic modulus along with an increase ina temperature or a decrease in a frequency. Among them, the relief dueto a microbrown movement of a molecular chain in an amorphous region isreferred to as main dispersion, and an extremely large relievingphenomenon is observed. A temperature at which this main dispersionoccurs is a glass transition point (Tg), and the viscoelasticityrelieving mechanism is most remarkably observed.

In the polymer composite piezoelectric body (the piezoelectric layer12), the polymer material of which the glass transition point is anormal temperature, in other words, the polymer material havingviscoelasticity at a normal temperature is used in the matrix, and thusthe polymer composite piezoelectric body which is rigid with respect toa vibration of 20 Hz to 20 kHz and is flexible with respect to avibration of less than or equal to a few Hz is realized. In particular,from a viewpoint of preferably exhibiting such behavior, it ispreferable that a polymer material of which the glass transitiontemperature at a frequency of 1 Hz is a normal temperature, that is, 0°C. to 50° C. is used in the matrix of the polymer compositepiezoelectric body.

As the polymer material having viscoelasticity at a normal temperature,various known materials are able to be used. Preferably, a polymermaterial of which the local maximum value of a loss tangent Tan δ at afrequency of 1 Hz at a normal temperature, that is, 0° C. to 50° C. in adynamic viscoelasticity test is greater than or equal to 0.5 is used.

Accordingly, in a case where the polymer composite piezoelectric body isslowly bent due to an external force, stress concentration on theinterface between the polymer matrix and the piezoelectric bodyparticles at the maximum bending moment portion is relieved, and thushigh flexibility is able to be expected.

In addition, it is preferable that, in the polymer material, a storageelastic modulus (E′) at a frequency of 1 Hz according to dynamicviscoelasticity measurement is greater than or equal to 100 MPa at 0° C.and is less than or equal to 10 MPa at 50° C.

Accordingly, it is possible to reduce a bending moment which isgenerated at the time of when the polymer composite piezoelectric bodyis slowly bent due to the external force, and it is possible to make thepolymer composite piezoelectric body rigid with respect to an acousticvibration of 20 Hz to 20 kHz.

In addition, it is more preferable that the relative permittivity of thepolymer material is greater than or equal to 10 at 25° C. Accordingly,in a case where a voltage is applied to the polymer compositepiezoelectric body, a higher electric field is applied to thepiezoelectric body particles in the polymer matrix, and thus a largedeformation amount is able to be expected.

However, in consideration of ensuring excellent moisture resistance orthe like, it is preferable that the relative permittivity of the polymermaterial is less than or equal to 10 at 25° C.

As the polymer material satisfying such conditions, cyanoethylatedpolyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate,polyvinylidene chloride-co-acrylonitrile, a polystyrene-vinylpolyisoprene block copolymer, polyvinyl methyl ketone, polybutylmethacrylate, and the like are exemplified.

In addition, a polymer material having a cyanoethyl group such as afluorine-based polymer such as polyvinylidene fluoride, a vinylidenefluoride-tetrafluoroethylene copolymer, a vinylidenefluoride-trifluoroethylene copolymer, a polyvinylidenefluoride-trifluoroethylene copolymer, and a polyvinylidenefluoride-tetrafluoroethylene copolymer, a polymer having a cyano groupor a cyanoethyl group such as a vinylidene cyanide-vinyl acetatecopolymer, cyanoethyl cellulose, cyanoethyl hydroxy saccharose,cyanoethyl hydroxy cellulose, cyanoethyl hydroxy pullulan, cyanoethylmethacrylate, cyanoethyl acrylate, cyanoethyl hydroxy ethyl cellulose,cyanoethyl amylose, cyanoethyl hydroxy propyl cellulose, cyanoethyldihydroxy propyl cellulose, cyanoethyl hydroxy propyl amylose,cyanoethyl polyacryl amide, cyanoethyl polyacrylate, cyanoethylpullulan, cyanoethyl polyhydroxy methylene, cyanoethyl glycidolpullulan, cyanoethyl saccharose, and cyanoethyl sorbitol, a syntheticrubber such as nitrile rubber or chloroprene rubber, and the like areexemplified.

In addition, as these polymer materials, a commercially availableproduct such as Hybrar 5127 (manufactured by Kuraray Co., Ltd.) is alsoable to be suitably used. Among them, a material having a cyanoethylgroup is preferably used, and cyanoethylated PVA is particularlypreferably used.

Furthermore, only one of these polymer materials may be used, or aplurality of types thereof may be used in combination (mixture).

The viscoelastic matrix 24 using such a polymer material havingviscoelasticity at a normal temperature, as necessary, may use aplurality of polymer materials in combination.

That is, in order to adjust dielectric properties or mechanicalproperties, other dielectric polymer materials may be added to theviscoelastic matrix 24 in addition to the viscoelastic material such ascyanoethylated PVA, as necessary.

As the dielectric polymer material which is able to be added to thematrix 24, for example, a fluorine-based polymer such as polyvinylidenefluoride, a vinylidene fluoride-tetrafluoroethylene copolymer, avinylidene fluoride-trifluoroethylene copolymer, a polyvinylidenefluoride-trifluoroethylene copolymer, and a polyvinylidenefluoride-tetrafluoroethylene copolymer, a polymer having a cyano groupor a cyanoethyl group such as a vinylidene cyanide-vinyl acetatecopolymer, cyanoethyl cellulose, cyanoethyl hydroxy saccharose,cyanoethyl hydroxy cellulose, cyanoethyl hydroxy pullulan, cyanoethylmethacrylate, cyanoethyl acrylate, cyanoethyl hydroxy ethyl cellulose,cyanoethyl amylose, cyanoethyl hydroxy propyl cellulose, cyanoethyldihydroxy propyl cellulose, cyanoethyl hydroxy propyl amylose,cyanoethyl polyacryl amide, cyanoethyl polyacrylate, cyanoethylpullulan, cyanoethyl polyhydroxy methylene, cyanoethyl glycidolpullulan, cyanoethyl saccharose, and cyanoethyl sorbitol, a syntheticrubber such as nitrile rubber or chloroprene rubber, and the like areexemplified.

Among them, a polymer material having a cyanoethyl group is suitablyused.

Furthermore, the dielectric polymer added to the viscoelastic matrix 24of the piezoelectric layer 12 in addition to the material havingviscoelasticity at a normal temperature such as cyanoethylated PVA isnot limited to one dielectric polymer, and a plurality of dielectricpolymers may be added.

In addition, in order to adjust the glass transition point Tg, athermoplastic resin such as a vinyl chloride resin, polyethylene,polystyrene, a methacrylic resin, polybutene, and isobutylene, and athermosetting resin such as a phenol resin, a urea resin, a melamineresin, an alkyd resin, and mica may be added in addition to thedielectric polymer material.

Furthermore, in order to improve pressure sensitive adhesiveness, aviscosity imparting agent such as rosin ester, rosin, terpene, terpenephenol, and a petroleum resin may be added.

In the viscoelastic matrix 24 of the piezoelectric layer 12, the addedamount at the time of adding a polymer in addition to the viscoelasticmaterial such as cyanoethylated PVA is not particularly limited, and itis preferable that a ratio of the added polymer to the viscoelasticmatrix 24 is less than or equal to 30 vol %.

Accordingly, it is possible to exhibit properties of the polymermaterial to be added without impairing the viscoelasticity relievingmechanism of the viscoelastic matrix 24, and thus a preferred result isable to be obtained from a viewpoint of increasing a dielectricconstant, of improving heat resistance, and of improving adhesivenessbetween the piezoelectric body particles 26 and the electrode layer.

In addition, for the purpose of increasing the dielectric constant ofthe piezoelectric layer 12, dielectric particles may be added to theviscoelastic matrix.

The dielectric particles are formed of particles having a relativepermittivity as high as 80 or more at 25° C.

As the dielectric particles, lead zirconate titanate (PZT), bariumtitanate (BaTiO₃), titanium oxide (TiO₂), strontium titanate (SrTiO₃),lead lanthanum zirconate titanate (PLZT), zinc oxide (ZnO), a solidsolution (BFBT) of barium titanate and bismuth ferrite (BiFeO₃), and thelike are exemplified. Among them, it is preferable to use bariumtitanate (BaTiO₃) as the dielectric particles from a viewpoint of havinga high relative permittivity.

It is preferable that the average particle diameter of the dielectricparticles is less than or equal to 0.5 μm.

In addition, the volume fraction of the dielectric particles withrespect to the total volume of the viscoelastic matrix and thedielectric particles is preferably 5% to 45%, more preferably 10% to30%, and particularly preferably 20% to 30%.

The piezoelectric body particles 26 are formed of ceramics particleshaving a perovskite type or wurtzite type crystal structure.

As the ceramics particles configuring the piezoelectric body particles26, for example, lead zirconate titanate (PZT), lead lanthanum zirconatetitanate (PLZT), barium titanate (BaTiO₃), zinc oxide (ZnO), a solidsolution (BFBT) of barium titanate and bismuth ferrite (BiFe₃), and thelike are exemplified.

Furthermore, only one type of these ceramics particles may be used, or aplurality of types thereof may be used in combination.

The particle diameter of the piezoelectric body particles 26 may beappropriately selected according to the size or usage of thetransduction film 10, and is preferably 1 μm to 10 μm according to theconsideration of the present inventors.

By setting the particle diameter of the piezoelectric body particles 26to be in the range described above, a preferred result is able to beobtained from a viewpoint of making high piezoelectric properties andflexibility compatible.

In addition, in FIG. 1, the piezoelectric body particles 26 in thepiezoelectric layer 12 are uniformly dispersed in the viscoelasticmatrix 24 with regularity. However, the present invention is not limitedthereto.

That is, in the viscoelastic matrix 24, the piezoelectric body particles26 in the piezoelectric layer 12 are preferably uniformly dispersed, andmay also be irregularly dispersed.

In the transduction film 10, a quantitative ratio of the viscoelasticmatrix 24 and the piezoelectric body particles 26 in the piezoelectriclayer 12 may be appropriately set according to the size in the surfacedirection or the thickness of the transduction film 10, the usage of thetransduction film 10, properties required for the transduction film 10,and the like.

Here, according to the consideration of the present inventors, thevolume fraction of the piezoelectric body particles 26 in thepiezoelectric layer 12 is preferably 30% to 70%, particularly preferablygreater than or equal to 50%. Therefore, the volume fraction thereof ismore preferably 50% to 70%.

By setting the quantitative ratio of the viscoelastic matrix 24 and thepiezoelectric body particles 26 to be in the range described above, itis possible to obtain a preferred result from a viewpoint of making highpiezoelectric properties and flexibility compatible.

In addition, in the transduction film 10, the thickness of thepiezoelectric layer 12 is also not particularly limited, and may beappropriately set according to the size of the transduction film 10, theusage of the transduction film 10, properties required for thetransduction film 10, and the like.

Here, according to the consideration of the present inventors, thethickness of the piezoelectric layer 12 is preferably 8 to 300 μm, morepreferably 8 to 40 μm, even more preferably 10 to 35 μm and particularlypreferably 15 to 25 μm.

By setting the thickness of the piezoelectric layer 12 to be in therange described above, it is possible to obtain a preferred result froma viewpoint of making ensuring rigidity and appropriate flexibilitycompatible.

Here, the piezoelectric layer 12 is subjected to electric polarizationprocessing (poling) and mechanical polarization processing.

By subjecting the piezoelectric layer 12 to the electric polarizationprocessing and mechanical polarization processing, in the case where thepiezoelectric layer 12 is evaluated by an X-ray diffraction method, theintensity ratio α₁ between the (002) plane peak intensity and the (200)plane peak intensity derived from the piezoelectric body particles ismore than or equal to 0.6 and less than 1.

The electric polarization processing, the mechanical polarizationprocessing, and the intensity ratio α₁ will be described later indetail.

As illustrated in FIG. 1, the transduction film 10 of the presentinvention has a configuration in which the lower thin film electrode 14is formed on one surface of the piezoelectric layer 12, the lowerprotective layer 18 is formed on the lower thin film electrode 14, theupper thin film electrode 16 is formed on the other surface of thepiezoelectric layer 12, the upper protective layer 20 is formed on theupper thin film electrode 16. Here, the upper thin film electrode 16 andthe lower thin film electrode 14 form an electrode pair.

In addition to these layers, the transduction film 10 may furtherinclude, for example, an electrode lead-out portion that leads out theelectrodes from the upper thin film electrode 16 and the lower thin filmelectrode 14, and an insulating layer which covers a region where thepiezoelectric layer 12 is exposed for preventing a short circuit or thelike.

As the electrode lead-out portion, the thin film electrode and theprotective layer are provided with parts protruding in a convex shape onthe outside in the surface direction of the piezoelectric layer.Alternatively, the electrode lead-out portion may be provided by forminga hole by removing a portion of the protective layer, inserting aconductive material such as a silver paste into the hole, andelectrically connecting the conductive material and the thin filmelectrode.

In each of the thin film electrodes, the number of electrode lead-outportions is not limited to one, and two or more electrode lead-outportions may be included. Particularly, in a case of the configurationin which the electrode lead-out portion is provided by removing aportion of the protective layer and inserting the conductive materialinto the hole, three or more electrode lead-out portions are provided toensure more reliable electrical connection.

That is, the transduction film 10 has a configuration in which bothsurfaces of the piezoelectric layer 12 are interposed between theelectrode pair, that is, the upper thin film electrode 16 and the lowerthin film electrode 14 and is further interposed between the upperprotective layer 20 and the lower protective layer 18.

The region interposed between the upper thin film electrode 16 and thelower thin film electrode 14 as described above is driven according toan applied voltage.

In the transduction film 10, the upper protective layer 20 and the lowerprotective layer 18 have a function of covering the upper thin filmelectrode 16 and the lower thin film electrode 14 and applyingappropriate rigidity and mechanical strength to the piezoelectric layer12. That is, there may be a case where, in the transduction film 10 ofthe present invention, the piezoelectric layer 12 consisting of theviscoelastic matrix 24 and the piezoelectric body particles 26 exhibitsextremely superior flexibility under bending deformation at a slowvibration but has insufficient rigidity or mechanical strength dependingon the usage. As a compensation for this, the transduction film 10 isprovided with the upper protective layer 20 and the lower protectivelayer 18.

In addition, since the lower protective layer 18 and the upperprotective layer 20 are different from each other only in position andhave the same configuration, in the following description, in a casewhere there is no need to distinguish between the lower protective layer18 and the upper protective layer 20, both the members are collectivelyreferred to as a protective layer.

The protective layer is not particularly limited, and may use varioussheet-like materials. As an example, various resin films are suitablyexemplified. Among them, by the reason of excellent mechanicalproperties and heat resistance, polyethylene terephthalate (PET),polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylenesulfite (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI),polyimide (PI), polyamide (PA), polyethylene naphthalate (PEN),triacetylcellulose (TAC), and a cyclic olefin-based resin are suitablyused.

The thickness of the protective layer is not particularly limited. Inaddition, the thicknesses of the upper protective layer 20 and the lowerprotective layer 18 may basically be identical to each other ordifferent from each other.

Here, in a case where the rigidity of the protective layer excessivelyincreases, not only is the stretching and contracting of thepiezoelectric layer 12 constrained, but also the flexibility isimpaired, and thus it is advantageous in a case where the thickness ofthe protective layer becomes thinner unless mechanical strength orexcellent handling ability as a sheet-like material is required.

Here, according to the consideration of the present inventors, in a casewhere the thickness of each of the upper protective layer 20 and thelower protective layer 18 is less than or equal to twice the thicknessof the piezoelectric layer 12, it is possible to obtain a preferredresult from a viewpoint of compatibility between ensuring of thestiffness and appropriate flexibility, or the like.

For example, in a case where the thickness of the piezoelectric layer 12is 50 μm and the lower protective layer 18 and the upper protectivelayer 20 are formed of PET, the thickness of each of the lowerprotective layer 18 and the upper protective layer 20 is preferably lessthan or equal to 100 μm, and more preferably less than or equal to 50μm, and particularly preferably less than or equal to 25 μm.

In the transduction film 10, the upper thin film electrode (hereinafter,also referred to as an upper electrode) 16 is formed between thepiezoelectric layer 12 and the upper protective layer 20, and the lowerthin film electrode (hereinafter, also referred to as a lower electrode)14 is formed between the piezoelectric layer 12 and the lower protectivelayer 18.

The upper electrode 16 and the lower electrode 14 are provided to applyan electric field to the transduction film 10 (the piezoelectric layer12).

In addition, since the lower electrode 14 and the upper electrode 16 aredifferent from each other only in size and position and have the sameconfiguration, in the following description, in a case where there is noneed to distinguish between the lower electrode 14 and the upperelectrode 16, both the members are collectively referred to as a thinfilm electrode.

In the present invention, a forming material of the thin film electrodeis not particularly limited, and as the forming material, variousconductive bodies are able to be used. Specifically, carbon, palladium,iron, tin, aluminum, nickel, platinum, gold, silver, copper, chromium,molybdenum, or an alloy thereof, indium-tin oxide, a conductive polymersuch as PEDOT/PPS (polyethylenedioxythiophene-polystyrene sulfonate) areexemplified. Among them, any one of copper, aluminum, gold, silver,platinum, and indium-tin oxide is suitably exemplified. From a viewpointof conductivity, costs, flexibility, and the like, copper is morepreferable.

In addition, a forming method of the protective layer is notparticularly limited, and as the forming method, various known methodssuch as a vapor-phase deposition method (a vacuum film forming method)such as vacuum vapor deposition or sputtering, film formation usingplating, a method of adhering a foil formed of the materials describedabove, and an application method are able to be used.

Among them, in particular, by the reason that the flexibility of thetransduction film 10 is able to be ensured, a copper or aluminum thinfilm formed by using the vacuum vapor deposition is suitably used as thethin film electrode. Among them, in particular, the copper thin filmformed by using the vacuum vapor deposition is suitably used.

The thicknesses of the upper electrode 16 and the lower electrode 14 arenot particularly limited. In addition, the thicknesses of the upperelectrode 16 and the lower electrode 14 may basically be identical toeach other or different from each other.

Here, like the protective layer described above, in a case where thestiffness of the thin film electrode excessively increases, not only isstretching and contracting of the piezoelectric layer 12 constrained,but also flexibility is impaired. For this reason, in a case where thethin film electrode is in a range where electrical resistance does notexcessively increase, it is advantageous as the thickness becomesthinner.

In addition, according to the consideration of the present inventors, ina case where the product of the thickness of the thin film electrode andthe Young's modulus is less than the product of the thickness of theprotective layer and the Young's modulus, the flexibility is notconsiderably impaired, which is suitable.

For example, in a case of a combination of the protective layer formedof PET (Young's modulus: approximately 6.2 GPa) and the thin filmelectrode formed of copper (Young's modulus: approximately 130 GPa), ina case where the thickness of the protective layer is 25 μm, thethickness of the thin film electrode is preferably less than or equal to1.2 μm, more preferably less than or equal to 0.3 μm, and particularlypreferably less than or equal to 0.1 μm.

As described above, the transduction film 10 has a configuration inwhich the piezoelectric layer 12 in which the piezoelectric bodyparticles 26 are dispersed in the viscoelastic matrix 24 havingviscoelasticity at a normal temperature is interposed between the upperelectrode 16 and the lower electrode 14 and is further interposedbetween the upper protective layer 20 and the lower protective layer 18.

In the transduction film 10, it is preferable that the local maximumvalue in which the loss tangent (Tan δ) at a frequency of 1 Hz accordingto the dynamic viscoelasticity measurement is greater than or equal to0.1 exists at a normal temperature.

Accordingly, even in a case where the transduction film 10 is subjectedto large bending deformation from the outside at a comparatively slowvibration of less than or equal to a few Hz, it is possible toeffectively diffuse the strain energy to the outside as heat, and thusit is possible to prevent a crack from being generated on the interfacebetween the polymer matrix and the piezoelectric body particles.

In the transduction film 10, it is preferable that the storage elasticmodulus (E′) at a frequency of 1 Hz according to the dynamicviscoelasticity measurement is 10 GPa to 30 GPa at 0° C., and 1 GPa to10 GPa at 50° C.

Accordingly, the transduction film 10 is able to have large frequencydispersion in the storage elastic modulus (E′) at a normal temperature.That is, the transduction film 10 is able to be rigid with respect to avibration of 20 Hz to 20 kHz, and is able to be flexible with respect toa vibration of less than or equal to a few Hz.

In addition, in the transduction film 10, it is preferable that theproduct of the thickness and the storage elastic modulus (E′) at afrequency of 1 Hz according to the dynamic viscoelasticity measurementis 1.0×10⁶ N/m to 2.0×10⁶ (1.0E+06 to 2.0E+06) N/m at 0° C., and 1.0×10⁵N/m to 1.0×10⁶ (1.0E+05 to 1.0E+06) N/m at 50° C.

Accordingly, the transduction film 10 is able to have appropriaterigidity and mechanical strength within a range not impairing theflexibility and the acoustic properties of the transduction film 10.

Furthermore, in the transduction film 10, it is preferable that the losstangent (Tan δ) at a frequency of 1 kHz at 25° C. is greater than orequal to 0.05 in a master curve obtained by the dynamic viscoelasticitymeasurement.

Accordingly, the frequency properties of the speaker using thetransduction film 10 become smooth, and thus it is also possible todecrease the changed amount of the acoustic quality at the time of whenthe lowest resonance frequency f₀ is changed according to the change inthe curvature of the speaker.

Here, in the transduction film 10 of the present invention, in the casewhere the polymer composite piezoelectric body as the piezoelectriclayer 12 is evaluated by the X-ray diffraction method, the intensityratio α₁=(002) plane peak intensity/((002) plane peak intensity+(200)plane peak intensity) between the (002) plane peak intensity and the(200) plane peak intensity derived from the piezoelectric body particlesis more than or equal to 0.6 and less than 1.

As described above, in a transduction film which uses, as apiezoelectric layer, a polymer composite piezoelectric body in whichpiezoelectric body particles are dispersed in a viscoelastic matrix, aferroelectric material such as PZT is used as the piezoelectric bodyparticles. The crystal structure of the ferroelectric material isdivided into many domains (domains) with different spontaneouspolarization directions. In this state, the spontaneous polarization ineach domain and the correspondingly generated piezoelectric effectcancel each other, so that no piezoelectric properties are seen as awhole.

Here, in the transduction film of the related art, the spontaneouspolarization directions of the domains are aligned by performingelectric polarization processing such as corona poling on thepiezoelectric layer and externally applying an electric field with acertain value or more. The piezoelectric body particles subjected to theelectric polarization processing exhibit the piezoelectric effect inresponse to the externally applied electric field. Accordingly, in theelectroacoustic transduction film, the transduction film itselfstretches and contracts in the surface direction thereof in response toan applied voltage and vibrates in a direction perpendicular to thesurface, thereby performing a conversion between a vibration (sound) andan electrical signal.

However, the spontaneous polarization directions of the domains(domains) (hereinafter, also simply referred to as the directions of thedomains) of the crystal structure of the ferroelectric material aredirected along not only the thickness direction of the transduction filmbut also various directions such as the surface direction. Therefore,even in the case where the electric polarization processing is performedby applying a higher voltage, not all the directions of the domainsdirected along the surface direction can be directed along the thicknessdirection in which the electric field is applied. In other words, 90°domains cannot be completely removed.

Therefore, in the transduction film in the related art, the domains inthe thickness direction of the transduction film (c domain) cannot befurther increased, and higher piezoelectric properties cannot beobtained.

In general, an X-ray diffraction method (XRD) is used as a method foranalyzing the crystal structure of such a piezoelectric layer(piezoelectric body particles), and the arrangement of atoms in crystalsis examined by XRD.

When a piezoelectric film in the related art was analyzed by an X-rayanalysis method (XRD), it was found that the intensity ratio α₁=(002)plane peak intensity/((002) plane peak intensity+(200) plane peakintensity) between a (002) plane peak intensity and a (200) plane peakintensity derived from the piezoelectric body particles is saturated ataround 0.55 even in a case where a poling electric field is increasedduring electric polarization processing, and a higher intensity ratio α₁cannot be obtained.

Here, the (002) plane peak intensity is a peak for a tetragonalstructure at around 43.5° in an XRD pattern obtained by XRD analysis,and the (200) plane peak intensity is a peak for a tetragonal structureat around 45° in an XRD pattern obtained by XRD analysis.

The XRD analysis can be performed using an X-ray diffraction apparatussuch as an X-ray diffractometer (Rint Ultima III manufactured by RigakuCorporation).

In addition, the (002) plane peak intensity corresponds to the ratio ofthe domains in the thickness direction of the transduction film (cdomains), and the (200) plane peak intensity corresponds to the ratio ofthe domains in the surface direction of the transduction film (adomains).

That is, the higher the intensity ratio α₁ (the higher the ratio of the(002) plane peak intensity), the higher the ratio of the domains in thethickness direction of the transduction film (c domains). Therefore,higher piezoelectric properties can be obtained.

On the other hand, in the transduction film of the present invention,since the intensity ratio α₁ between the (002) plane peak intensity andthe (200) plane peak intensity derived from the piezoelectric bodyparticles in the case where the polymer composite piezoelectric body asthe piezoelectric layer 12 is evaluated by the X-ray diffraction methodis more than or equal to 0.6 and less than 1, the ratio of the domains(c domains) in the thickness direction of the transduction film is high,and higher piezoelectric properties can be obtained. Therefore, theconversion efficiency between a vibration (sound) and an electricalsignal can be further increased. Accordingly, in a case where thetransduction film is used as a vibration plate of a speaker, the speakercan reproduce a sound with a sufficient sound volume. Furthermore, sincethe conversion efficiency is high, power consumption can be reduced.

Furthermore, as in the transduction film in the related art, in the casethe ratio of the domains in the surface direction is high and a drivingvoltage is applied, the 90° domain wall is moved, which causeshysteresis of distortion. Therefore, there is concern that distortionmay occur in the reproduced sound.

On the other hand, in the transduction film of the present invention,since the ratio of the domains in the surface direction (a domains) islow, in the case where the driving voltage is applied, 90° domain motiondecreases, and thus the distortion in the reproduced sound decreases.

In addition, as a method of obtaining a piezoelectric layer with anintensity ratio α₁ of more than or equal to 0.6 in a case where thepiezoelectric layer is evaluated by XRD, there is a method of performingelectric polarization processing and thereafter performing mechanicalpolarization processing. It is assumed that by further performing themechanical polarization processing after performing the electricpolarization processing, the domains in the surface direction of thetransduction film (a domains) can be allowed to be directed along thethickness direction, and thus the ratio of the domains in the thicknessdirection (c domains) can be increased.

The electric polarization processing and the mechanical polarizationprocessing will be described later in detail.

Here, the intensity ratio α₁ is more preferably 0.67 to 0.75.

By setting the intensity ratio α₁ to be in this range, higherpiezoelectric properties can be obtained, and the conversion efficiencycan be further increased.

In a case where the driving voltage is applied, the domains directedalong the surface direction (a domains) may rotate to be directed alongthe thickness direction (the direction in which the driving voltage isapplied). Since such 90° domain motion has power, the presence of thiseffect further increases the piezoelectric properties, and thepiezoelectric properties become higher than in a case where all thedomains are directed along the thickness direction.

Therefore, the piezoelectric properties can be further increased byleaving the domains directed along the surface direction (a domains) ina predetermined proportion by setting the intensity ratio α₁ to be equalto or lower than 0.75.

Next, the manufacturing method of an electroacoustic transduction filmof the present invention will be described.

The manufacturing method of an electroacoustic transduction film of thepresent invention is a manufacturing method of an electroacoustictransduction film including a polymer composite piezoelectric body inwhich piezoelectric body particles are dispersed in a viscoelasticmatrix formed of a polymer material having viscoelasticity at a normaltemperature, two thin film electrodes laminated on both surfaces of thepolymer composite piezoelectric body, and two protective layersrespectively laminated on the two thin film electrodes. Themanufacturing method of an electroacoustic transduction film includes: apreparation step of preparing electrode laminated bodies in each ofwhich one of the thin film electrodes and one of the protective layersare laminated; a first lamination step of producing a first laminatedbody by laminating one of the electrode laminated bodies and the polymercomposite piezoelectric body; an electric polarization processing stepof performing electric polarization processing on the polymer compositepiezoelectric body of the first laminated body; a second lamination stepof producing a second laminated body by laminating the other electrodelaminated body on the surface of the polymer composite piezoelectricbody on which no electrode laminated body is laminated; and a mechanicalpolarization processing step of performing mechanical polarizationprocessing on the second laminated body.

Hereinafter, an example of a manufacturing method of the transductionfilm 10 will be described with reference to FIGS. 2A to 2E and FIG. 3.

The preparation step is a step of preparing the electrode laminated bodyin which the single thin film electrode and the single protective layerare laminated.

First, as illustrated in FIG. 2A, a lower electrode laminated body 11 awhich is a sheet-like material in which the lower electrode 14 is formedon the lower protective layer 18 is prepared.

In addition, as illustrated in FIG. 2E, an upper electrode laminatedbody 11 c which is a sheet-like material in which the upper thin filmelectrode 16 and the upper protective layer 20 are laminated isprepared.

The lower electrode laminated body 11 a may be prepared by forming acopper thin film or the like as the lower thin film electrode 14 on thesurface of the lower protective layer 18 using vacuum vapor deposition,sputtering, plating, and the like.

Similarly, the upper electrode laminated body 11 c may be prepared byforming a copper thin film or the like as the upper thin film electrode16 on the surface of the upper protective layer 20 using vacuum vapordeposition, sputtering, plating, and the like.

In a case where the protective layer is extremely thin, and thus thehandleability is degraded, the protective layer with a separator(temporary supporter) may be used. As the separator, a PET film having athickness of approximately 25 to 100 μm, and the like are able to beused. The separator may be removed after thermal compression bonding ofthe thin film electrode and the protective layer immediately beforeforming a side surface insulating layer, a second protective layer, andthe like.

The first lamination step is the step of producing the first laminatedbody by laminating the lower electrode laminated body and the polymercomposite piezoelectric body.

Specifically, the first laminated body 11 b in which the lower electrodelaminated body 11 a and the piezoelectric layer 12 are laminated isproduced by applying a coating composition that is to become thepiezoelectric layer 12 onto the lower electrode 14 of the lowerelectrode laminated body 11 a and thereafter curing the coatingcomposition to form the piezoelectric layer 12.

First, a coating material is prepared by dissolving a polymer material(hereinafter, also referred to as a viscoelastic material) havingviscoelasticity at a normal temperature, such as cyanoethylated PVA, inan organic solvent, further adding the piezoelectric body particles 26such as PZT particles thereto, and stirring and dispersing theresultant. The organic solvent is not particularly limited, and as theorganic solvent, various organic solvents such as dimethylformamide(DMF), methyl ethyl ketone, and cyclohexanone are able to be used.

In a case where the lower electrode laminated body 11 a described aboveis prepared and the coating material is prepared, the coating materialis cast (applied) onto the lower electrode laminated body 11 a, and theorganic solvent is evaporated and dried. Accordingly, as illustrated inFIG. 2B, the first laminated body 11 b in which the lower thin filmelectrode 14 is provided on the lower protective layer 18 and thepiezoelectric layer 12 is laminated on the lower thin film electrode 14is prepared.

A casting method of the coating material is not particularly limited,and as the casting method, all known methods (coating devices) such as aslide coater or a doctor blade are able to be used.

Alternatively, in a case where the viscoelastic material is a materialthat is able to be heated and melted like cyanoethylated PVA, a meltedmaterial is prepared by heating and melting the viscoelastic materialand adding and dispersing the piezoelectric body particles 26 therein,is extruded into a sheet shape on the lower electrode laminated body 11a illustrated in FIG. 2A by extrusion molding or the like, and iscooled, thereby preparing the first laminated body 11 b as illustratedin FIG. 2B.

In addition, as described above, in the transduction film 10, inaddition to the viscoelastic material such as cyanoethylated PVA, apolymer piezoelectric material such as PVDF may be added to theviscoelastic matrix 24.

In the case where the polymer piezoelectric material is added to theviscoelastic matrix 24, the polymer piezoelectric material added to thecoating material may be dissolved. Alternatively, the polymerpiezoelectric material to be added may be added to the heated and meltedviscoelastic material and may be heated and melted.

The electric polarization processing step is the step of performingelectric polarization processing (poling) on the piezoelectric layer 12of the first laminated body 11 b in which the lower electrode 14 isprovided on the lower protective layer 18 and the piezoelectric layer 12is formed on the lower electrode 14.

An electric polarization processing method of the piezoelectric layer 12is not particularly limited, and a known method is able to be used. As apreferred electric polarization processing method, an electricpolarization processing method using corona poling illustrated in FIGS.2C and 2D is exemplified.

In this method, as illustrated in FIGS. 2C and 2D, for example, a gap gof 1 mm is opened on an upper surface 12 a of the piezoelectric layer 12of the first laminated body 11 b, and a rod-like or wire-like coronaelectrode 30 which is able to be moved along the upper surface 12 a isprovided. Then, the corona electrode 30 and the lower electrode 14 areconnected to a direct-current power source 32.

Furthermore, heating means for heating and holding the first laminatedbody 11 b, for example, a hot plate, is prepared.

Then, in a state where the piezoelectric layer 12 is heated and held bythe heating means, for example, at a temperature of 100° C., adirect-current voltage of a few kV, for example, 6 kV, is appliedbetween the lower electrode 14 and the corona electrode 30 from thedirect-current power source 32, and thus a corona discharge occurs.Furthermore, in a state where the gap g is maintained, the coronaelectrode 30 is moved (scanned) along the upper surface 12 a of thepiezoelectric layer 12, and the piezoelectric layer 12 is subjected tothe electric polarization processing.

During the electric polarization processing using the corona discharge(hereinafter, also referred to as corona poling processing), knownrod-like moving means may be used to move the corona electrode 30.

In addition, in the corona poling processing, a method of moving thecorona electrode 30 is not limited. That is, the corona electrode 30 isfixed, a moving mechanism for moving the first laminated body 11 b isprovided, and the polarization processing may be performed by moving thefirst laminated body 11 b. Moving means for a known sheet-like materialmay be used to move the first laminated body 11 b.

Furthermore, the number of corona electrodes 30 is not limited to one,and the corona poling processing may be performed by using a pluralityof corona electrodes 30.

In addition, the electric polarization processing is not limited to thecorona poling processing, and normal electric field poling in which adirect-current electric field is directly applied to an object to besubjected to the electric polarization processing may also be used.However, in a case where this normal electric field poling is performed,it is necessary that the upper electrode 16 is formed before theelectric polarization processing.

Before the electric polarization processing, calender processing may beperformed to smoothen the surface of the piezoelectric layer 12 using aheating roller or the like. By performing the calender processing, asecond lamination step described below is able to be smoothly performed.

By the electric polarization processing, domains (180° domains) directedalong the direction opposite to the direction in which the electricfield is applied in the thickness direction are switched, that is, 180°domain motion is generated to align the directions of the domains in thethickness direction.

In the example described above, the corona discharge voltage is set toda direct-current voltage of 6 kV but is not limited thereto. The coronadischarge voltage may be appropriately set according to the propertiesrequired for the transduction film, the material and thickness of eachlayer of the transduction film, and the like.

The second lamination step is the step of producing the second laminatedbody 11 d by laminating the upper electrode laminated body 11 c on thesurface of the piezoelectric layer 12 (polymer composite piezoelectricbody) of the first laminated body 11 b on which the lower electrodelaminated body 11 a is laminated.

As illustrated in FIG. 2E, the upper electrode laminated body 11 cprepared in the preparation step is laminated on the piezoelectric layer12 side of the first laminated body 11 b subjected to the polarizationprocessing while the upper electrode 16 faces the piezoelectric layer12.

A method of bonding the first laminated body 11 b and the upperelectrode laminated body 11 c to each other is not particularly limited,and a method using an adhesive, a thermal compression bonding methodusing a heating press device, a heating roller pair, or the like may beused.

In a case where the first laminated body 11 b and the upper electrodelaminated body 11 c are bonded together using an adhesive, the materialof the adhesive is not particularly limited, and a known adhesive usedfor adhesion between the piezoelectric layer and the thin film electrodein the transduction film can be appropriately used. The same polymermaterial as the material of the viscoelastic matrix may be used as theadhesive.

The mechanical polarization processing step is the step of performingmechanical polarization processing on the second laminated body 11 dprepared in the second lamination step.

Specifically, the mechanical polarization processing is processing inwhich the proportion of the c domains directed along the thicknessdirection is increased by applying shear stress to the piezoelectriclayer 12 of the second laminated body 11 d and thus reducing theproportion of the a domains directed along the surface direction.

The reason that the proportion of the c domains is increased by applyingthe shear stress of the piezoelectric layer 12 is presumed as follows.

In the case where the shear stress is applied to the piezoelectric layer12 (the piezoelectric body particles 26), the piezoelectric bodyparticles 26 are forced to stretch in the longitudinal direction(thickness direction). At this time, 90° domain motion is generated, andthe a domains directed along the surface direction are directed alongthe thickness direction and become c domains. In addition, thedirections of the c domains directed along the thickness direction arenot changed. As a result, it is assumed that the proportion of the adomains is reduced and thus the proportion of the c domains isincreased.

As described above, by reducing the proportion of the a domains and thusincreasing the c domains through the mechanical polarization processing,the intensity ratio α₁ between the (002) plane peak intensity and the(200) plane peak intensity derived from the piezoelectric body particlesis allowed to be more than or equal to 0.6 in the case where thepiezoelectric layer 12 is evaluated by the X-ray diffraction method, andhigher piezoelectric properties can be obtained.

Here, in the present invention, the mechanical polarization processingis performed after the electric polarization processing.

The 90° domain motion generated by the mechanical polarizationprocessing is more likely to be generated as the 180° domain wall iseliminated.

Therefore, the 180° domain motion is generated by the electricpolarization processing, the 180° domain motion is eliminated to cause astate in which the 90° domain motion is more likely to be generated, andthereafter the mechanical polarization processing is performed, wherebythe 90° domain motion is generated, the a domains directed along thesurface direction are directed along the thickness direction and becomethe c domains, and thus the proportion of the c domains can beincreased.

As a method of applying shear stress to the piezoelectric layer 12 asthe mechanical polarization processing, a method of pressing a rolleragainst one surface side of the second laminated body 11 d asillustrated in FIG. 3 can be cited.

In the case where the shear stress is applied to the piezoelectric layer12 using the roller, the type of the roller is not particularly limited,and a rubber roller, a metal roller, or the like can be appropriatelyused.

The value of the shear stress applied to the piezoelectric layer 12 isnot particularly limited, and may be appropriately set according to theproperties required for the transduction film, the material andthickness of each layer of the transduction film, and the like.

In the case where the piezoelectric layer 12 is evaluated by the X-raydiffraction method, the intensity ratio α₁ between the (002) plane peakintensity and the (200) plane peak intensity derived from thepiezoelectric body particles can be adjusted to be in a range of morethan or equal to 0.67 and less than or equal to 0.75. From thisviewpoint, the shear stress applied to the piezoelectric layer 12 ispreferably set to 0.3 MPa to 0.5 MPa.

The shear stress applied to the piezoelectric layer 12 may be obtainedby dividing the applied shear load by the cross-sectional area parallelto the shear load, or by detecting tensile strain or compressive straincaused by the compressive stress and calculating shear stress from thedetection result.

In addition, in the case where the shear stress is applied to thepiezoelectric layer 12 using the roller, the temperature of thetransduction film and the roller is preferably set to 20° C. to 130° C.,and more preferably set to 50° C. to 100° C. In a case where thetemperature is too high, the polymer material becomes too soft totransmit the shear force. In a case where the temperature is low, thepolymer material is too hard to change the domain ratio. Therefore, itis considered that by maintaining a temperature at which the polymermaterial has an appropriately soft state, the domain ratio can be easilychanged.

Next, an electroacoustic transducer using the electroacoustictransduction film of the present invention will be described withreference to FIGS. 4A and 4B.

FIG. 4A is a front view conceptually illustrating an electroacoustictransducer 40, and FIG. 4B is a sectional view taken along line B-B inFIG. 4A.

The electroacoustic transducer 40 uses the transduction film 10 as avibration plate.

In the electroacoustic transducer 40, in a case where the transductionfilm 10 is stretched in an in-plane direction due to the application ofa voltage to the transduction film 10, the transduction film 10 movesupward (in the radial direction of sound) in order to absorb thestretching. Conversely, in a case where the transduction film 10 iscontracted in the in-plane direction due to application of a voltage tothe transduction film 10, the transduction film 10 moves downward(toward a case 42) in order to absorb the contraction. Theelectroacoustic transducer 40 performs a conversion between a vibration(sound) and an electrical signal by the vibrations caused by repetitionof stretching and contraction of the transduction film 10.

The electroacoustic transducer 40 is configured to include thetransduction film 10, the case 42, a viscoelastic supporter 46, and apressing member 48.

The case 42 is a holding member that holds the transduction film 10 andthe viscoelastic supporter 46 together with the pressing member 48, andis a box-shaped case which is formed of plastic, metal, wood, or thelike and has an open surface. As illustrated in the figure, the case 42has a thin hexahedral shape, and one of the largest surfaces is the opensurface. The open portion has a regular quadrilateral shape. The 42accommodates the viscoelastic supporter 46 therein.

The viscoelastic supporter 46 has moderate viscosity and elasticity,holds the transduction film 10 in a bent state, and imparts a constantmechanical bias at any place of the transduction film 10 to efficientlyconvert the stretching and contracting movement of the transduction film10 into a forward and rearward movement (a movement in the directionperpendicular to the surface of the transduction film).

In the illustrated example, the viscoelastic supporter 46 has aquadrangular prism shape having a bottom surface shape substantiallyequal to the bottom surface of the case 42. In addition, the height ofthe viscoelastic supporter 46 is larger than the depth of the case 42.

The material of the viscoelastic supporter 46 is not particularlylimited as long as the material has moderate viscosity and elasticityand suitably deforms without impeding the vibration of the piezoelectricfilm. As an example, wool felt, nonwoven fabric of wool felt includingrayon or PET, a foamed material (foamed plastic) such as glass wool orpolyurethane, polyester wool, a laminate of a plurality of sheets ofpaper, a magnetic fluid, a coating material, and the like areexemplified.

The specific gravity of the viscoelastic supporter 46 is notparticularly limited and may be appropriately selected according to thetype of the viscoelastic supporter. As an example, in a case where feltis used as the viscoelastic supporter, the specific gravity thereof ispreferably 50 to 500 kg/m³, and more preferably 100 to 300 kg/m³. In acase where glass wool is used as the viscoelastic supporter, thespecific gravity thereof is preferably 10 to 100 kg/m³.

The pressing member 48 is for supporting the transduction film 10 in astate of being pressed against the viscoelastic supporter 46, and is amember formed of plastic, metal, wood, or the like in a regularquadrilateral shape with an opening at the center. The pressing member48 has the same shape as the open surface of the case 42, and the shapeof the opening is the same regular quadrilateral shape as the openportion of the case 42.

The electroacoustic transducer 40 is configured by accommodating theviscoelastic supporter 46 in the case 42, covering the case 42 and theviscoelastic supporter 46 with the transduction film 10, and fixing thepressing member 48 to the case 42 in a state in which the periphery ofthe transduction film 10 is brought into contact with the open surfaceof the case 42 by the pressing member 48.

A method of fixing the pressing member 48 to the case 42 is notparticularly limited, and various known methods such as a method usingscrews or bolts and nuts and a method using a holding device are able tobe used.

In the electroacoustic transducer 40, the height (thickness) of theviscoelastic supporter 46 is greater than the height of the innersurface of the case 42. That is, in a state before the transduction film10 and the pressing member 48 are fixed, the viscoelastic supporter 46is in a state protruding from the upper surface of the case 42.

Therefore, in the electroacoustic transducer 40, the viscoelasticsupporter 46 is held in a state in which the viscoelastic supporter 46is pressed downward by the transduction film 10 and decreases inthickness toward the peripheral portion of the viscoelastic supporter46. That is, at least a portion of the principal surface of thetransduction film 10 is held in a bent state. Accordingly, a bentportion is formed in at least a portion of the transduction film 10. Inthe electroacoustic transducer 40, the bent portion serves as avibration surface. In the following description, the bent portion isalso referred to as a vibration surface.

At this time, it is preferable that the entire surface of theviscoelastic supporter 46 is pressed in the surface direction of thetransduction film 10 so that the thickness decreases over the entiresurface. That is, it is preferable that the entire surface of thetransduction film 10 is pressed and supported by the viscoelasticsupporter 46.

In addition, it is preferable that the bent portion formed in this waygradually changes in curvature from the center to the peripheralportion. Accordingly, the resonance frequencies are distributed,resulting in a wider band.

In addition, in the electroacoustic transducer 40, the viscoelasticsupporter 46 is in a state of being compressed more in the thicknessdirection as it approaches the pressing member 48. However, due to thestatic viscoelastic effect (stress relaxation), a constant mechanicalbias can be maintained at any place of the transduction film 10.Accordingly, the stretching and contracting movement of the transductionfilm 10 is efficiently converted into a forward and rearward movement,so that it is possible to obtain a flat electroacoustic transducer 40that is thin, achieves a sufficient sound volume, and has excellentacoustic properties.

In the electroacoustic transducer 40 having such a configuration, aregion of the transduction film 10 corresponding to the opening of thepressing member 48 serves as the bent portion that actually vibrates.That is, the pressing member 48 is a portion that defines the bentportion.

In an electroacoustic transducer which uses a transduction film havingpiezoelectric properties, it is easy to increase the relative size of avibration plate to the entire unit compared to a cone speaker generallyhaving a circular vibration plate, and miniaturization is facilitated.

From the above viewpoint, the width of the edge portion of the pressingmember 48 is preferably less than or equal to 20 mm, and preferably 1 mmto 10 mm.

Furthermore, it is preferable that the surface of the electroacoustictransducer 40 on the transduction film 10 side and the bent portion aresimilar. That is, it is preferable that the outer shape of the pressingmember 48 and the shape of the opening are similar.

In addition, in the electroacoustic transducer 40, the pressing force ofthe viscoelastic supporter 46 against the transduction film 10 is notparticularly limited, and is 0.005 to 1.0 MPa and particularlypreferably about 0.02 to 0.2 MPa in terms of surface pressure at aposition where the surface pressure is low.

Moreover, although the thickness of the viscoelastic supporter 46 is notparticularly limited, the thickness thereof before being pressed is 1 to100 mm, and particularly preferably 10 to 50 mm.

In the illustrated example, the configuration in which the viscoelasticsupporter 46 having viscoelasticity is used is provided, but is notlimited thereto, and a configuration using an elastic supporter havingat least elasticity may be provided.

For example, a configuration including an elastic supporter havingelasticity instead of the viscoelastic supporter 46 may be provided.

As the elastic supporter, natural rubber and various synthetic rubbersare exemplified.

Here, in the electroacoustic transducer 40 illustrated in FIG. 4A, theentire peripheral area of the transduction film 10 is pressed againstthe case 42 by the pressing member 48, but the present invention is notlimited thereto.

That is, the electroacoustic transducer using the transduction film 10is also able to use a configuration in which the transduction film 10 ispressed against and fixed to the upper surface of the case 42 by screws,bolts and nuts, holding devices, or the like, for example, at the fourcorners of the case 42 without using the pressing member 48.

An O-ring or the like may be interposed between the case 42 and thetransduction film 10. With this configuration, a damper effect is ableto be achieved, and it is possible to prevent the vibration of thetransduction film 10 from being transmitted to the case 42, and toobtain excellent acoustic properties.

In addition, the electroacoustic transducer using the transduction film10 may not have the case 42 that accommodates the viscoelastic supporter46.

That is, for example, as conceptually illustrated by a sectional view ofan electroacoustic transducer 50 in FIG. 5, the viscoelastic supporter46 is placed on a support plate 52 having rigidity, the transductionfilm 10 is placed to cover the viscoelastic supporter 46, the samepressing member 48 as described above is placed on the peripheralportion thereof. Next, a configuration in which the pressing member 48is fixed to the support plate 52 by screws 54 or the like to press theviscoelastic supporter 46 together with the pressing member 48 is alsoable to be used.

The size of the support plate 52 may be greater than the viscoelasticsupporter 46. Furthermore, by using various vibration plates formed ofpolystyrene, foamed PET, or carbon fiber as the material of the supportplate 52, an effect of further amplifying the vibration of theelectroacoustic transducer can be expected.

Moreover, the electroacoustic transducer is not limited to theconfiguration that presses the periphery, and for example, aconfiguration in which the center of the laminated body of theviscoelastic supporter 46 and the transduction film 10 is pressed bysome means is also able to be used.

That is, various configurations are able to be used by theelectroacoustic transducer as long as the transduction film 10 is heldin a bent state.

Alternatively, a configuration in which a resin film is attached to thetransduction film 10 to apply tension thereto (bend) may also beadopted. By configuring the transduction film 10 to be held with theresin film and causing the transduction film 10 to be held in a bentstate, a flexible speaker is able to be obtained.

Alternatively, the transduction film 10 may be configured to bestretched over a bent frame.

In the example illustrated in FIGS. 4A and 4B, the configuration inwhich the transduction film 10 is pressed against the viscoelasticsupporter 46 so as to be supported using the pressing member 48 isprovided, but is not limited thereto. For example, a configuration inwhich the end portion of the transduction film is fixed to the rearsurface side of the case 42 using the transduction film 10 which islarger than the open surface of the case 42 may be provided. That is,the case 42 and the viscoelastic supporter 46 disposed in the case 42may be covered with the transduction film 10 which is larger than theopen surface of the case 42, the end portion of the transduction film 10may be pulled toward the rear surface side of the case 42 so thetransduction film 10 is pressed against the viscoelastic supporter 46 tobe bent with tension, and the end portion of the transduction film maybe fixed to the rear surface side of the case 42.

Alternatively, for example, a configuration in which an airtight case isused, the open end of the case is covered and closed by the transductionfilm, gas is introduced into the case to apply a pressure to thetransduction film, and the transduction film is thus held in a convexlyswollen state may be provided.

For example, an electroacoustic transducer 56 illustrated in FIG. 6C isexemplified.

First, as illustrated in FIG. 6A, the electroacoustic transducer 56 usesan object having airtightness as the same case 42 and is provided with apipe 42 a for introducing air into the case 42.

An O-ring 57 is provided on the upper surface of the end portion on theopen side of the case 42 and is covered with the transduction film 10 toclose the open surface of the case 42.

Next, as illustrated in FIG. 6B, a frame-shaped pressing lid 58 havingan inner periphery substantially the same as the outer periphery of thecase 42 and an approximately L-shaped cross section is fitted to theouter periphery of the case 42 (the O-ring 57 is omitted in FIGS. 6B and6C).

Accordingly, the transduction film 10 is pressed against and fixed tothe case 42 such that the inside of the case 42 is airtightly closed bythe transduction film 10.

Furthermore, as illustrated in FIG. 6C, air is introduced from the pipe42 a into the case 42 (a closed space formed by the case 42 and thetransduction film 10) to apply a pressure to the transduction film 10,and the transduction film 10 is thus held in a convexly swollen state,thereby forming the electroacoustic transducer 56.

The pressure in the case 42 is not limited, and may be the atmosphericpressure or higher such that the transduction film 10 is convexlyswollen.

The pipe 42 a may be fixed or detachable. In a case where the pipe 42 ais detached, it is natural that the detaching portion of the pipe isairtightly closed.

In FIG. 6C, the configuration in which the transduction film 10 is heldin the convexly swollen state by applying the pressure to the case isprovided. However, as illustrated in FIG. 6D, a configuration in whichthe same airtight case as in FIG. 6C is used, the open end of the caseis covered and closed by the transduction film, the case is degassed toapply a negative pressure to the transduction film, and the transductionfilm is thus held in a concave state.

Next, a flexible display which is a flexible sheet-like image displaydevice and uses the electroacoustic transduction film of the presentinvention as a speaker will be described.

Specifically, the flexible display is a flexible display with a speaker,in which the transduction film 10 of the present invention is attachedas a speaker to the rear surface of a flexible sheet-like display device(the surface on the opposite side of an image display surface) such as aflexible organic EL display device, a flexible liquid crystal displaydevice, or a flexible electronic paper.

The flexible display of the present invention may be a color display ora monochrome display.

As described above, the transduction film 10 of the present inventionhas excellent flexibility and has no in-plane anisotropy. Therefore, thetransduction film 10 of the present invention has little change inacoustic quality even in a case where the transduction film 10 is bentin any direction and also has little change in acoustic quality with achange in curvature.

Therefore, the flexible display with a speaker of the present inventionformed by attaching the transduction film 10 of the present invention tothe flexible image display device has excellent flexibility and canoutput a sound with stable acoustic quality regardless of a bendingdirection or bending amount due to the state held by a hand (that is, tosuitably correspond to arbitrary deformation).

Various embodiments of the flexible display which uses theelectroacoustic transduction film of the present invention as thespeaker will be described with reference to FIGS. 7A to 7C.

FIG. 7A is a sectional view conceptually illustrating an example of theflexible display of the present invention in which the electroacoustictransduction film of the present invention is used in an organic EL(electroluminescence) display.

An organic EL display 60 illustrated in FIG. 7A is an organic ELflexible display with a speaker formed by attaching the transductionfilm 10 of the present invention to the rear surface of a flexiblesheet-like organic EL display device 62.

In the flexible display of the present invention, a method of attachingthe transduction film 10 of the present invention to the rear surface ofa flexible sheet-like image display device such as the organic ELdisplay device 62 is not limited. That is, any known method of attaching(bonding) sheet-like materials surface-to-surface to each other can beused.

As an example, a bonding method using an adhesive, a bonding methodusing thermal fusion, a method using a double-sided tape, a method usingan adhesive tape, a method using a holding device that holds the endportions or end edges of a plurality of laminated sheet-like materials,such as a substantially C-shaped clamp, a method using a holding devicethat holds the insides of the surfaces (excluding an image displaysurface) of a plurality of laminated sheet-like materials, such as arivet, a method of holding both surfaces of a plurality of laminatedsheet-like materials with protective films (at least the image displayside is transparent), a method using the above methods in combination,and the like are exemplified.

In a case where the display device and the transduction film 10 arebonded to each other using an adhesive or the like, the entire surfacesmay be bonded, only the entire peripheries of the end portions may bebonded, spots at appropriately set points such as four corners andcenter portions may be bonded, or these methods may be used incombination.

In the organic EL display 60, the transduction film 10 is the(electroacoustic) transduction film 10 of the present inventiondescribed above which is configured to have the piezoelectric layer 12formed of the polymer composite piezoelectric body, the lower thin filmelectrode 14 provided on one surface of the piezoelectric layer 12, theupper thin film electrode 16 provided on the other surface, the lowerprotective layer 18 provided on the surface of the lower thin filmelectrode 14, and the upper protective layer 20 provided on the surfaceof the upper thin film electrode 16, and is configured such that theintensity ratio α₁=(002) plane peak intensity/((002) plane peakintensity+(200) plane peak intensity) between the (002) plane peakintensity and the (200) plane peak intensity derived from thepiezoelectric body particles is more than or equal to 0.6 and less than1.

On the other hand, the organic EL display device 62 is a known flexiblesheet-like organic EL display device (organic EL display panel).

That is, as an example, the organic EL display device 62 is configuredto have, on a substrate 64 formed of a plastic film or the like, ananode 68 in which a pixel electrode having a switching circuit such as aTFT is formed, have a light-emitting layer 70 which uses an organic ELmaterial on the anode 68, a transparent cathode 72 made of ITO (indiumtin oxide) on the light-emitting layer 70, and have a transparentsubstrate 74 formed of a transparent plastic on the cathode 72.

In addition, a hole injection layer or a hole transport layer may beprovided between the anode 68 and the light-emitting layer 70, and anelectron transport layer or an electron injection layer may be furtherprovided between the light-emitting layer 70 and the cathode 72.Furthermore, a protective film such as a gas barrier film may beprovided on the transparent substrate 74.

Although not illustrated in the figure, wires for driving thetransduction film 10, that is, the speaker are connected to the lowerelectrode 14 and the upper electrode 16 of the transduction film 10.Furthermore, wires for driving the organic EL display device 62 areconnected to the anode 68 and the cathode 72.

These points are also applied to an electronic paper 78, a liquidcrystal display 94, and the like, which will be described later.

FIG. 7B conceptually illustrates an example of the flexible display ofthe present invention in which the electroacoustic transduction film ofthe present invention is used in an electronic paper.

The electronic paper 78 illustrated in FIG. 7B is an electronic paperwith a speaker formed by attaching the transduction film 10 of thepresent invention to the rear surface of a flexible sheet-likeelectronic paper device 80.

In the electronic paper 78, the transduction film 10 is the same as thatdescribed above.

On the other hand, the electronic paper device 80 is a known flexibleelectronic paper. That is, as an example, the electronic paper device 80is configured to have, on a substrate 82 made of a plastic film or thelike, a lower electrode 84 in which a pixel electrode having a switchingcircuit such as a TFT is formed, have a display layer 86 in whichpositively or negatively charged microcapsules 86 a containing a whiteor black pigment are arranged on the lower electrode 84, have atransparent upper electrode 90 made of ITO or the like on the displaylayer 86, and have a transparent substrate 92 formed of a transparentplastic on the upper electrode 90.

The example illustrated in FIG. 7B is an example in which the flexibledisplay of the present invention is used in the electrophoretic typeelectronic paper using the microcapsules. However, the present inventionis not limited thereto.

That is, the flexible display of the present invention may use any typeof known electronic paper, such as an electrophoretic type in which nomicrocapsules are used, an electrophoretic type, a chemical change typeusing a redox reaction or the like, an electronic granular body type, anelectrowetting type, or a liquid crystal type as long as the electronicpaper is in the form of a sheet having flexibility.

FIG. 7C conceptually illustrates an example in which the electroacoustictransduction film of the present invention is used in a liquid crystaldisplay.

The liquid crystal display 94 illustrated in FIG. 7C is a liquid crystalflexible display with a speaker formed by attaching the transductionfilm 10 of the present invention to the rear surface of a flexiblesheet-like liquid crystal display device 96.

In the liquid crystal display 94, the transduction film 10 is the sameas that described above.

On the other hand, the liquid crystal display device 96 is a knownflexible sheet-like liquid crystal display device (liquid crystaldisplay panel). That is, as an example, the liquid crystal displaydevice 96 has a flexible edge light type light guide plate 98 and alight source 100 that receives the backlight from the end portion of thelight guide plate 98. As an example, the liquid crystal display device96 is configured to have a polarizer 102 on the light guide plate 98,have a transparent lower substrate 104 on the polarizer 102, have, onthe lower substrate 104, a transparent lower electrode 106 in which apixel electrode having a switching circuit such as a TFT is formed, havea liquid crystal layer 108 on the lower electrode 106, have atransparent upper electrode 110 made of ITO or the like on the liquidcrystal layer 108, a transparent upper substrate 112 on the upperelectrode 110, a polarizer 114 on the upper substrate 112, and aprotective film 116 on the polarizer 114.

The flexible display of the present invention is not limited to theorganic EL display, the electronic paper, and the liquid crystaldisplay, and an image display apparatus using various display devicescan be used as long as the display devices are flexible sheet-likedisplay devices (display panels).

Next, a configuration in which the electroacoustic transduction film ofthe present invention is used as a microphone or a sensor for a musicalinstrument will be described.

The transduction film 10 of the present invention having thepiezoelectric layer 12 in which the piezoelectric body particles aredisposed in a polymer matrix having viscoelasticity at a normaltemperature, the lower thin film electrode 14 and the upper thin filmelectrode 16 provided on the surfaces of the piezoelectric layer 12, andthe lower protective layer 18 and the upper protective layer 20respectively provided on the surfaces of the thin film electrodes, thepiezoelectric layer 12 also has a capability of converting vibrationenergy into an electrical signal.

Therefore, the transduction film 10 of the present invention can also besuitably used in the microphone or sensor for a musical instrument(pickup) using this.

As an example, a vocal cord microphone is suitably exemplified.

FIG. 8 conceptually illustrates an example of a general vocal cordmicrophone.

As illustrated in FIG. 8, a general vocal cord microphone 120 in therelated art has a complex configuration in which a piezoelectric ceramic126 such as PZT is laminated on a metal plate 128 such as a brass plate,elastic cushions 130 and a spring 132 are respectively attached to thelower surface and the upper surface of this laminated body and aresupported in a case 124, and signal lines 134 and 136 are drawn out fromthe case.

Contrary to this, the vocal cord microphone of the present invention inwhich the transduction film 10 of the present invention is used as asensor for converting a sound signal into an electrical signal can beconfigured as a vocal cord microphone, for example, with a simpleconfiguration in which means for attaching the transduction film 10 isprovided and only a signal line for extracting the electrical signaloutput from the piezoelectric layer 12 (the lower electrode 14 and theupper electrode 16) is provided.

In addition, the vocal cord microphone of the present invention havingsuch a configuration acts as a vocal cord microphone only by attachingthe transduction film 10 to the vicinity of the vocal cord.

Furthermore, the vocal cord microphone in the related art in which thepiezoelectric ceramic 126 and the metal plate 128 are used asillustrated in FIG. 8 has a very small loss tangent, so that resonancetends to be very strong and frequency properties extremely fluctuate,resulting in a metallic tone.

Contrary to this, as described above, since the transduction film 10 ofthe present invention has excellent flexibility and acoustic propertiesand has little change in acoustic quality during deformation, thetransduction film 10 of the present invention can be attached to thethroat of a person with a complex curved surface and can reliablyreproduce low to high frequency sounds.

That is, according to the present invention, an ultralight andspace-saving vocal cord microphone can be realized with a simpleconfiguration in which a sound signal extremely close to a voice can beoutput and does not cause a wearing sensation.

In the vocal cord microphone of the present invention, a method ofattaching the transduction film 10 to the vicinity of the vocal cord isnot particularly limited, and various known methods of attaching asheet-like material can be used.

Alternatively, instead of attaching the transduction film 10 directly tothe vicinity of the vocal cord, the transduction film 10 may beaccommodated in an extremely thin case or a bag and then attached to thevicinity of the vocal cord.

In addition, the sensor for a musical instrument of the presentinvention which uses the transduction film 10 of the present inventionas a sensor for converting a sound signal into an electrical signal canbe configured as a sensor for a musical instrument, for example, with asimple configuration in which means for attaching the transduction film10 is provided and only a signal line for extracting the electricalsignal output from the piezoelectric layer 12 (the lower electrode 14and the upper electrode 16) is provided.

Furthermore, the sensor for a musical instrument of the presentinvention having such a configuration acts as a pickup only by attachingthe transduction film 10 to the case surface of a musical instrument.

Like the vocal cord microphone described above, since the transductionfilm 10 of the present invention is thin and sufficiently flexible, thesensor for a musical instrument of the present invention has excellentflexibility and acoustic properties and has little change in acousticquality during deformation. Therefore, the transduction film 10 of thepresent invention can be attached to the case surface of a musicalinstrument with a complex curved surface and can reliably reproduce thesound of the musical instrument at low to high frequencies.

Furthermore, the sensor for a musical instrument of the presentinvention has little mechanical restraint on the case surface of themusical instrument and thus can minimize the influence of the attachmentof the pickup on the original sound of the musical instrument.

Like the vocal cord microphone described above, in the sensor for amusical instrument of the present invention, a method of attaching thesensor for a musical instrument to a musical instrument is notparticularly limited, and various known methods of attaching asheet-like material can be used. Alternatively, in the sensor for amusical instrument of the present invention, the transduction film 10may be accommodated in an extremely thin case or a bag and then attachedto the musical instrument.

As described above, the electroacoustic transduction film of the presentinvention, the manufacturing method thereof, the electroacoustictransducer, the flexible display, the vocal cord microphone, and thesensor for a musical instrument are described in detail, but the presentinvention is not limited to the examples described above, and variousimprovements or modifications may be performed within a range notdeviating from the gist of the present invention.

EXAMPLES

Hereinafter, the present invention will be described in more detail withreference to specific examples of the present invention. The presentinvention is not limited the examples, and the materials, use amounts,proportions, processing contents, processing procedures, and the likedescribed in the following examples can be appropriately modifiedwithout departing from the gist of the present invention.

Example 1

According to the method illustrated in FIGS. 2A to 2E and FIG. 3described above, the transduction film 10 illustrated in FIG. 1 wasprepared.

(Preparation Step)

A lower electrode laminated body 11 a and an upper electrode laminatedbody 11 c in each of which a copper thin film having a thickness of 0.1μm was vacuum vapor deposited on a PET film having a thickness of 4 μmwere prepared. That is, in this example, the upper electrode 16 and thelower electrode 14 are copper vapor deposition thin films having athickness of 0.1 μm, and the upper protective layer 20 and the lowerprotective layer 18 are PET films having a thickness of 4 μm.

In order to obtain good handleability during the process, as the PETfilm, a film with a separator (temporary supporter PET) having athickness of 50 μm attached thereto was used, and the separator of eachprotective layer was removed after the thermal compression bonding ofthe upper electrode laminated body 11 c.

(First Lamination Step)

First, cyanoethylated PVA (CR-V manufactured by Shin-Etsu Chemical Co.,Ltd.) was dissolved in methyl ethyl ketone (MEK) at the followingcompositional ratio. Thereafter, PZT particles were added to thissolution at the following compositional ratio, and were dispersed byusing a propeller mixer (rotation speed 2000 rpm), and thus a coatingmaterial for forming the piezoelectric layer 12 was prepared.

PZT Particles 300 parts by mass Cyanoethylated PVA  15 parts by mass MEK 85 parts by mass

In addition, the PZT particles were obtained by sintering commerciallyavailable PZT raw material powder at 1000° C. to 1200° C. and thereaftercrushing and classifying the resultant so as to have an average particlediameter of 5 μm.

The coating material for forming the piezoelectric layer 12 prepared asdescribed above was applied onto the lower electrode 14 (the coppervapor deposition thin film) of the lower electrode laminated body 11 aprepared in advance by using a slide coater. Furthermore, the coatingmaterial was applied such that the film thickness of the coating filmafter being dried was 20 μm.

Next, a material in which the coating material was applied onto thelower electrode laminated body 11 a was heated and dried in an on a hotplate at 120° C. such that MEK was evaporated. Accordingly, the firstlaminated body 11 b was prepared in which the lower electrode 14 made ofcopper was provided on the lower protective layer 18 made of PET and thepiezoelectric layer 12 (polymer composite piezoelectric body) having athickness of 20 μm was formed thereon.

(Electric Polarization Processing Step)

The electric polarization processing was performed on the piezoelectriclayer 12 of the first laminated body 11 b by the corona polingillustrated in FIGS. 2C and 2D described above. Furthermore, theelectric polarization processing was performed by setting thetemperature of the piezoelectric layer 12 to 100° C., and applying adirect-current voltage of 6 kV between the lower electrode 14 and thecorona electrode 30 so as to cause corona discharge to occur.

(Second Lamination Step)

The upper electrode laminated body 11 c was laminated on the firstlaminated body 11 b which was subjected to the electric polarizationprocessing while the upper electrode 16 (copper thin film side) facedthe piezoelectric layer 12.

Next, the laminated body of the first laminated body 11 b and the upperelectrode laminated body 11 c was subjected to thermal compressionbonding at 120° C. by using a laminator device, and thus thepiezoelectric layer 12 adhered to the upper electrode 16 and the lowerelectrode 14 such that the second laminated body 11 d was prepared.

(Mechanical Polarization Processing Step)

Next, the mechanical polarization processing was performed by applyingshear stress to the prepared second laminated body 11 d using a rubberroller (urethane rubber with a SUS core) such that the transduction film10 was prepared.

The shear stress applied to the piezoelectric layer 12 was set to 0.2MPa.

<Measurement of Intensity Ratio>

Regarding the prepared transduction film, the XRD pattern for thecrystal structure of the piezoelectric body particles 26 in thepiezoelectric layer 12 was measured by the X-ray diffraction method(XRD) using the X-ray diffractometer (Rint Ultima III manufactured byRigaku Corporation) (see FIG. 10).

From the measured XRD pattern, the (002) plane peak intensity at around43.5° and the (200) plane peak intensity at around 45° were read, andthe intensity ratio α₁=(002) plane peak intensity/((002) plane peakintensity+(200) plane peak intensity) between the (002) plane peakintensity and the (200) plane peak intensity was obtained.

The intensity ratio α₁ was 0.600.

Examples 2 to 8

The electroacoustic transduction film 10 was prepared in the same manneras in Example 1 except that the shear stress applied to thepiezoelectric layer 12 in the mechanical polarization processing stepwas changed to values shown in Table 1.

In addition, the XRD pattern of each of the prepared transduction filmswas measured in the same manner as in Example 1, and the intensity ratioα₁ was obtained.

Comparative Example 1

An electroacoustic transduction film was prepared in the same manner asin Example 1 except that the electric polarization processing and themechanical polarization processing were not performed.

In addition, the XRD pattern of the prepared transduction film wasmeasured in the same manner as in Example 1, and the intensity ratio α₁was obtained.

Comparative Examples 2 to 4

An electroacoustic transduction film was prepared in the same manner asin Example 1 except that the mechanical polarization processing was notperformed and the corona discharge voltage in the electric polarizationprocessing step was changed as shown in Table 1.

In addition, the XRD pattern of each of the prepared transduction filmswas measured in the same manner as in Example 1, and the intensity ratioα₁ was obtained.

[Evaluation]

<Sound Pressure Sensitivity>

(Preparation of Electroacoustic Transducer)

A circular test piece of ϕ70 mm was cut from the prepared transductionfilm 10 and was assembled into the case 42 to prepare theelectroacoustic transducer 56 b as illustrated in FIG. 6D, and the soundpressure sensitivity thereof was measured.

The case 42 is a cylindrical container having an open surface, and aplastic cylindrical container having an open surface size of ϕ60 mm anda depth of 10 mm was used.

The transduction film 10 was disposed so as to cover the opening of thecase 42 and the peripheral portion thereof was fixed by the pressing lid58. Thereafter, air in the case 42 was evacuated from the pipe 42 a tomaintain the pressure in the case 42 at 0.09 MPa such that thetransduction film 10 was bent in a concave shape.

(Measurement of Sound Pressure)

The sound pressure level of the prepared electroacoustic transducer wasmeasured to obtain the sound pressure sensitivity.

Specifically, as illustrated in FIG. 9, a microphone P was placed toface the center of the transduction film 10 of an electroacoustictransducer 56 b at a position of 0.5 m apart therefrom, a sine wave at 1kHz and 1 W was input between the upper electrode and the lowerelectrode of the electroacoustic transducer, and the sound pressurelevel was measured and converted into a sound pressure sensitivity.

Evaluation results are shown in Table 1.

In addition, the XRD pattern of Examples 1, 4, and 6 and ComparativeExample 1 are shown in FIG. 10.

A graph showing the relationship between the value of the obtained soundpressure sensitivity and the intensity ratio α₁ is shown in FIG. 11A,and FIG. 11B shows an enlarged graph of a region with an intensity ratioα₁ of more than or equal to 0.5.

TABLE 1 Electric polarization processing Mechanical Evaluation Coronapolarization Sound discharge processing Intensity pressure voltage Shearstress ratio sensitivity kV MPa α1 dB/(W · m) Example 1 6 0.2 0.60074.00 Example 2 6 0.3 0.670 78.60 Example 3 6 0.4 0.720 79.50 Example 46 0.5 0.750 78.50 Example 5 6 0.6 0.794 77.90 Example 6 6 0.8 0.83175.90 Example 7 6 1 0.880 74.20 Example 8 6 2 0.950 69.00 Comparative −− 0.342 26.20 Example 1 Comparative 3 − 0.367 30.50 Example 2Comparative 6 − 0.516 68.10 Example 3 Comparative 8 − 0.521 68.30Example 4

It can be seen from Table 1 that the sound pressure sensitivity inExamples 1 to 8 of the electroacoustic transduction film of the presentinvention is further improved compared to that in Comparative Examples 1to 4.

In addition, as can be seen from the graph shown in FIG. 10, it can beseen that the (002) plane peak intensity can be increased by performingthe electric polarization processing and the mechanical polarizationprocessing.

Furthermore, as can be seen from the graphs in FIGS. 11A and 11B,regarding the correlation between the intensity ratio α₁ between the(002) plane peak intensity and the (200) plane peak intensity derivedfrom the piezoelectric body particles and the sound pressuresensitivity, it can be seen that the more the intensity ratio α₁, thehigher the sound pressure sensitivity, and a peak appears at around anintensity ratio α₁ of 0.7.

In addition, it can be seen from the comparison between ComparativeExamples 2 to 4 that by performing only the electric polarizationprocessing, the intensity ratio α₁ is increased only to about 0.55 evenwhen the corona discharge voltage is further increased.

On the other hand, it can be seen from the examples that by performingthe mechanical polarization processing after performing the electricpolarization processing, the intensity ratio α₁ can be increased to 0.6or more, and thus the sound pressure sensitivity can be improved.

In addition, it can be seen from the comparison between Examples 1 to 8that by setting the intensity ratio α₁ to be in a range of 0.67 to 0.75,the sound pressure sensitivity can be more than or equal to 78 dB/(W·m),which is preferable.

In addition, it can be seen that it is preferable to set the shearstress applied to the piezoelectric layer during the mechanicalpolarization processing to be in a range of 0.3 to 0.5 MPa.

From the above results, the effect of the present invention is obvious.

EXPLANATION OF REFERENCES

-   -   10: electroacoustic transduction film    -   11 a: lower electrode laminated body    -   11 b: first laminated body    -   11 c: upper electrode laminated body    -   11 d: second laminated body    -   12: piezoelectric layer    -   14: lower thin film electrode    -   16: upper thin film electrode    -   18: lower protective layer    -   20: upper protective layer    -   24: viscoelastic matrix    -   26: piezoelectric body particles    -   30: corona electrode    -   32: direct-current power source    -   40, 50, 56, 56 b: electroacoustic transducer    -   42, 124: case    -   46: viscoelastic supporter    -   48: pressing member    -   52: support plate    -   54: screw    -   57: O-ring    -   58: pressing lid    -   60: organic EL display    -   62: organic EL display device    -   64, 82: substrate    -   68: anode    -   70: light-emitting layer    -   72: cathode    -   74, 92: transparent substrate    -   78: electronic paper    -   80: electronic paper device    -   84, 106: lower electrode    -   86: display layer    -   86 a: microcapsule    -   90, 110: upper electrode    -   94: liquid crystal display    -   96: liquid crystal display device    -   98: light guide plate    -   100: light source    -   102, 114: polarizer    -   104: lower substrate    -   108: liquid crystal layer    -   112: upper substrate    -   116: protective film    -   120: vocal cord microphone    -   126: piezoelectric ceramic    -   128: metal plate    -   130: cushion    -   132: spring    -   134, 136: signal line

What is claimed is:
 1. An electroacoustic transduction film comprising: a polymer composite piezoelectric body in which piezoelectric body particles are dispersed in a viscoelastic matrix formed of a polymer material having viscoelasticity at a normal temperature; two thin film electrodes laminated on both surfaces of the polymer composite piezoelectric body; and two protective layers respectively laminated on the two thin film electrodes, wherein an intensity ratio □1=(002) plane peak intensity/((002) plane peak intensity+(200) plane peak intensity) between a (002) plane peak intensity and a (200) plane peak intensity derived from the piezoelectric body particles in a case where the polymer composite piezoelectric body is evaluated by an X-ray diffraction method is more than or equal to 0.6 and less than
 1. 2. The electroacoustic transduction film according to claim 1, wherein the intensity ratio □1 is more than or equal to 0.67 and less than or equal to 0.75.
 3. The electroacoustic transduction film according to claim 1, wherein a relative permittivity of the polymer material is more than or equal to 10 at 25□C.
 4. The electroacoustic transduction film according to claim 1, wherein the piezoelectric body particles are formed of ceramics particles having a perovskite type or wurtzite type crystal structure.
 5. The electroacoustic transduction film according to claim 3, wherein the piezoelectric body particles are formed of ceramics particles having a perovskite type or wurtzite type crystal structure.
 6. The electroacoustic transduction film according to claim 1, wherein the piezoelectric body particles are formed of ceramics particles having at least one of lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO₃), zinc oxide (ZnO), and a solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe₃).
 7. An electroacoustic transducer comprising: the electroacoustic transduction film according to claim
 1. 8. A flexible display comprising: the electroacoustic transduction film according to claim 1 attached to a surface of the flexible display having flexibility, the surface being opposite to an image display surface. 